California Code, Labor Code - LAB § 973

If any person advertises for, or seeks employees by means of newspapers, posters, letters, or otherwise, or solicits or communicates by letter or otherwise with persons to work for him or the person for whom he is acting, or to work at any shop, plant, or establishment while a strike, lockout, or other trade dispute is still in active progress at such shop, plant, or establishment, he shall plainly and explicitly mention in such advertisement or oral or written solicitations or communications that a strike, lockout, or other labor disturbance exists.

The person inserting any such advertisement, solicitation, or communication in a newspaper, on a poster, or otherwise, shall insert in such advertisement, solicitation or communication his own name and, if he is representing another, the name of the person he is representing and at whose direction and under whose authority he is inserting the advertisement, solicitation or communication. The appearance of this name in connection with such advertisement, solicitation or communication is prima facie evidence as to the person responsible for the advertisement, solicitation or communication.